On Monday, February 03, 2014 at 09:54:33 PM, Eric Nelson wrote:
Hi Marek,
On 02/03/2014 01:16 PM, Marek Vasut wrote:
On Monday, February 03, 2014 at 08:57:30 PM, Eric Nelson wrote:
[...]
I like having this bit included, but do you need to attribute copyright for this block?
I'd hate to tempt PCISIG with this portion actually. That's why I didn't put the whole quotation into the patch either.
[...]
We really should start waving a sign "YOU MUST CONNECT PERST IN YOUR NEW DESIGN, OTHERWISE A KITTEN DIES!"
Hey, leave the kittens alone!
Are ponies ok? Friendship is magic afterall :-)
We have had success in using/testing PCIe devices without either, but that doesn't mean we match the spec, and I suppose we'll have to live with the "broken design" message...
I know. The design without FR works most of the time, but there is one particular scenario where it may fail (means it fails reliably). I will assume we have just a simple RC<->EP connection with EP being i82574L card (well supported and easily available intel NIC):
- Cold boot the system
- Bring up the PCIe link in U-Boot
- Use the e1000e driver for some transfer
- Boot Linux
- Bring up the PCIe link in Linux
- Use the e1000e driver for some transfer
- Reboot the system from Linux
- Bring up the PCIe link in U-Boot
In case you don't have means to do FR, your system will fail during 5) and/or during 8) because in either case, the link and/or EP device can be in undefined state from previous usage. You are therefore not able to send in-band messages to the EP (to issue hot reset for example*) nor restart the link, thus you're trapped.
- if you try to send anything over unstable PCIe link on MX6, it can
stall your entire system to the point where the system bus is stuck and not even JTAG debugger can halt the CPU (!)
Thanks. That's a useful test scenario.
Hope it helps :) Sometimes you need to do a few cycles until the hardware hangs. I found this out when I was debugging another custom board here. I think we will have a rock-solid PCIe implementation on MX6 for 3.14 and 2014.04 ;-)
Best regards, Marek Vasut